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Politics : PRESIDENT GEORGE W. BUSH

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To: joseph krinsky who wrote (240671)	3/21/2002 5:04:39 PM
From: Kenneth V. McNutt	Read Replies (1) of 769670

DESIGN CRITERIA Nuclear facilities are designed so that earthquakes and other external events will not jeopardize the safety of the plant. Because of the frequency and magnitude of earthquakes in Japan, particular attention is paid to seismic issues in the siting, design and construction of nuclear power plants. The seismic design of such plants is based on criteria far more stringent than those applying to non-nuclear facilities. Japanese nuclear power plants are designed to withstand two earthquake ground motion waves, S1 and S2.* * The same ground motion at reactor site could result from an earthquake near the site or a larger earthquake at a greater distance. The design basis earthquake ground motion S1 is defined as the largest earthquake ground motion which can reasonably be expected to occur at the site of a nuclear power plant during its lifetime, based on the known seismicity of the area. A power reactor could continue to operate safely during an S1 level earthquake. Larger earthquake ground motions in the region, considering the tectonic structures and other factors, must also be taken into account, although their probability is very low. The largest conceivable such ground motion is the design basis earthquake ground motion S2. The plant's safety systems would be effective during an S2 level earthquake to ensure safe shutdown without release of radioactivity. Nuclear power plants are fitted with seismic detectors. If these register ground motions of a set level, usually less than S1 to allow a margin for extra safety, systems will be activated to automatically bring the plant to a safe shutdown. Power reactors are also built on hard rock foundations to minimise seismic shaking. After the Kobe earthquake a panel was set up to review the safety of nuclear facilities and the design guidelines for their construction. The Nuclear Safety Commission then approved the panel's report. After recalculating the seismic design criteria required for a nuclear power plant to survive near the epicentre of a large earthquake it concluded that under current guidelines such a plant could survive a quake of 7.75 on the Richter scale. The Kobe quake was 7.2. More info. Ken

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